1. Field of the Invention
Embodiments relates to a method of controlling an access to a channel in a wireless communication system.
2. Description of the Related Art
A wireless local area network (WLAN) employs a scheme of preoccupying channels by dispersively accessing a channel medium through a distributed coordination function (DCF) or an enhanced distributed channel access (EDCA), and of transmitting a frame. However, as a number of stations in a basic service set (BSS) including an access point (AP) and a plurality of stations increases, a dispersive channel occupation method has a limitation. When a large number of stations may attempt to access channels to occupy limited resources, a collision probability and a transmission wait time may be rapidly increased.
In the Institute of Electrical and Electronics Engineers (IEEE) 802.11ah, connections of up to 8,000 stations need to be supported. It is impossible to assign different time slots to 8,000 stations, respectively. In the IEEE 802.11ah, a set of a plurality of time slots is called a “restricted access window (RAW),” and the RAW may be assigned to a specific station group. A finite number of time slots in the RAW may be assigned to stations of the specific station group, and each of the stations may perform connection only in a time slot assigned to each of the stations.
Because a plurality of stations may be assigned to a single slot, one of the stations may fail to use the slot. When a station to which an earlier slot in the RAW is assigned fails to occupy a medium in the earlier slot, the station may attempt to access a channel in a next slot using a DCF scheme, which may cause an issue of a related art to occur.
In an existing channel access method based on the IEEE 802.11ah, contention resolution may not be appropriately performed when a plurality of stations are assigned to a single RAW. This is because stations failing to occupy channels in a previous slot continue to appear as new contenders in a next slot.
Because a minimum value of a backoff counter of each of stations failing to occupy a channel in a previous slot is highly likely to be maintained, a collision may occur due to transmission of a plurality of stations in a next slot. Due to the collision, a garbage packet may be highly likely to be generated. The garbage packet may not be decoded by an AP or a destination device. Accordingly, a technology for solving the above issue is required.